New research shows that soon after doctors started prescribing a drug (Spironolactone, also known as Aldactone) for congestive heart failure more widely, the number of patients who died from a side effect increased. The researchers say their findings illustrate what can happen when doctors apply drug-study results to their own patients. They suggest that some of the patients probably shouldn't have been given the heart failure drug and that doctors weren't checking for dangerous potassium buildup.